The present invention relates to a light-emitting device and to an electronic apparatus having the light-emitting device. More particularly, the present invention relates to a protective circuit of a light-emitting device.
A light-emitting device has a plurality of scanning lines, a plurality of data lines, light-emitting elements provided at intersections of the plurality of scanning lines and the plurality of data lines, a current supply line that supplies current to the light-emitting elements, and driving transistors that are provided on current paths from the current supply line to the light-emitting elements so as to control the current to the light-emitting elements. A plurality of unit circuits, each having at least the light-emitting element and a driving transistor, are arranged in a line or in a matrix shape. The light-emitting elements emit light according to selection signals from the scanning lines and data signals from the data lines.
In such a light-emitting device, a part or an entity of a scanning line driving circuit that supplies the selection signals to the scanning lines or a data line driving circuit that supplies the data signals to the data lines is incorporated into a substrate, where the light-emitting elements are provided, so as to serve as an internal circuit, or is attached to the substrate so as to serve as an external IC circuit. The scanning line driving circuit or the data line driving circuit may be deteriorated or destroyed for various reasons. In particular, a problem is caused by stress due to electrostatic discharge, that is, electrostatic destruction, which occurs while the light-emitting device is being manufactured or transported.
At least one of the scanning line driving circuit and the data line driving circuit may be incorporated into the substrate and a circuit, such as a driving power supply circuit which supplies power to them, a timing control circuit, or the like, may be constructed as an external IC circuit. Further, at least one of the scanning line driving circuit and the data line driving circuit of the substrate may be connected to the external IC circuit. In this case, in a manufacturing process of connecting the substrate to the external IC circuit, electrostatic charge flows in at least one of the scanning line driving circuit and the data line driving circuit formed on the substrate, which causes the circuit to be destroyed. Further, connecting terminals that connect at least one of the scanning line driving circuit and the data line driving circuit of the substrate to the external IC circuit may be provided on the substrate. In this case, electrostatic charge may flow in the light-emitting device through the connecting terminals. If the electrostatic charge is applied to wiring lines which are connected to the driving circuit, the driving circuit may be deteriorated or destroyed.
In order to prevent such deterioration or destruction of the driving circuit due to electrostatic charge, a protective circuit is provided on a signal path through which a signal is input/output in the driving circuit (see Japanese Unexamined Patent Application Publication Nos. 10-294383 and 2003-308050). More specifically, the protective circuit may be provided as an input protective circuit for an input terminal, to which various signals including clock signals, inversion clock signals, start pulses, and the like are input from the outside of the driving circuit. Alternatively, the protective circuit may be provided as an output protective circuit for an output terminal, through which various signals including scanning signals, end pulses, and the like are output to the outside of the driving circuit.
Further, a technique in which, in an insulated-gate-type transistor circuit, electrostatic charge accumulated in a floating portion of the circuit is effectively discharged so as to prevent destruction of an element due to the electrostatic charge has been suggested (for example, see Japanese Unexamined Patent Application Publication No. 2000-98338).
Further, in addition to the above-described techniques, various techniques for protecting various display devices from electrostatic charge has been suggested (for example, see Japanese Unexamined Patent Application Publication Nos. 9-80469, 10-39325, 11-72806, and 2000-89685).
As described above, the light-emitting device has, for example, the plurality of scanning lines, the plurality of data lines, the light-emitting elements provided at the intersections of the plurality of scanning lines and the plurality of data lines, the current supply line that supplies the current to the light-emitting elements, and the driving transistors that are provided on the current paths from the current supply line to the light-emitting elements so as to control the current to the light-emitting elements. In particular, the current supply line is thicker than other wiring lines and is connected to the current supply source and the light emitting elements with low resistance so as to supply the current to the light-emitting elements. Further, when the unit circuits are formed in a line or in a matrix shape, each unit circuit having at least the light-emitting element and the driving transistor, the current supply line needs to have low resistance so that the plurality of unit circuits uniformly emit.
However, if the current supply line is made to have low resistance in such a manner, the electrostatic charge reaches the unit circuits via the current supply line, which results in the unit circuits being deteriorated or destroyed due to electrostatic destruction. In particular, when each unit circuit includes an element having two conductive layers with a dielectric film interposed therebetween, insulation breakdown may occur in the dielectric film, such that the unit circuit may be deteriorated or destroyed. As the element having two conductive layers with the dielectric film interposed therebetween, for example, a MOS field effect transistor or a capacitive element is exemplified.
Further, a unit circuit in which the current flows from the current supply line to the data line, a predetermined potential is written into a gate of the driving transistor, and a current according to the voltage flows in the light-emitting element has been suggested. Such a method is referred to as a current programming method. In addition, the current programming method is broadly divided into a method in which the predetermined potential is written into the gate of the driving transistor by allowing the current to flow via the driving transistor of the unit circuit, and a method in which the predetermined potential is written into the gate of the driving transistor by allowing the current to flow via a mirror transistor which constitutes a mirror circuit together with the driving transistor. In such a current programming method, it is necessary to make the current supply line have low resistance and also to make the data line have low resistance such that the predetermined potential is accurately written into the data line. In this case, however, the electrostatic charge may reach the unit circuit via the data line.
In particular, there is a case in which a current supply circuit that supplies current to the current supply line or the data line driving circuit is constituted by an external IC circuit and the light-emitting elements of the substrate are connected to the external IC circuit. In this case, however, the electrostatic charge may reach the unit circuits from the connecting terminals that connect the light-emitting elements of the substrate to the external IC circuit.
As described above, various transistors included in the unit circuits may be destroyed due to an unexpected voltage caused by the electrostatic charge from the current supply line and the data lines. Accordingly, the yield in a manufacturing process of the light-emitting device may be decreased. In particular, organic electroluminescent (EL) elements are current-driven-type light-emitting elements, and thus it is important to suppress the unexpected voltage caused by the electrostatic charge from the current supply line or the data lines from being applied to the unit circuits, while ensuring a path through which a driving current or a data signal is supplied to the unit circuit.
As such, in the light-emitting device, the yield of the light-emitting device in the manufacturing process may be enhanced by reducing electrostatic destruction of the element included in the unit circuit due to the electrostatic charge. In this case, however, the current path, through which the driving current or the data signal is supplied to the unit circuit, for a high-quality image display cannot be ensured, while simultaneously enhancing the yield. In the Japanese Unexamined Patent Application Publications described above, as for the current-driven-type light-emitting device, there is no description about the two points described above.